Study Looks at Effect of Exercise on Diabetes in NIH Staff

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BETHESDA, MD—For years now, physicians have been imploring the nation to get more exercise. Pointing to research showing great benefits in overall health and in combating chronic disease, researchers have also been pressing employers to include exercise and nutrition programs into the workplace. The theory is that an exercising workforce is a healthier, happier, and more productive workforce. Also, with the cost of insurance rising due to the need to treat chronic diseases, a healthier workforce is a less expensive one.

Employees as Research Subjects

In 2004, NHLBI undertook a commitment to put its research where its mouth is, establishing a worksite wellness program called Keep-the-Beat. The program encouraged heart-healthy behaviors, and included physical and nutrition activities for all NHLBI employees. Physical activity rooms were installed in several NIH buildings, and interested employees were given pedometers. Health stations were set up where employees could measure their blood pressure and weigh themselves.

The following year, a fellow working at NHLBI took note of the program and suggested opening a research protocol to measure the effects of the program on vascular disease.

“At the time the protocol’s primary focus was on the endothelium,” explained Dr Richard Cannon, NHLBI clinical director at an NIH symposium on diabetes and heart health last month. “[The focus was] on the idea that participation in the program could mobilize bone-marrow derived cells—called endothelial progenitor cells.”

Researchers believed those cells would be pushed out of the bone marrow into the blood stream and attach themselves to diseased or damaged endothelium, helping repair it.

“What we learned was that sedentary employees of the clinical center entering the Keep-the-Beat program were overweight or obese [with] many cardiovascular risk factors,” Cannon explained.

The study showed a reduction in blood pressure, as well as in total LDL and HDL cholesterol. “We did see increased EPCs, but only a small contribution to improved endothelial function.”

Examining Insulin Resistance

Believing studying employees in the program might yield even more data, Cannon and his colleagues wrote a second protocol. This one looked at other vascular functions that might be improved by the program, including changes in insulin sensitivity, high-density lipoprotein function and adipokines—cell-to-cell signaling proteins secreted by adipose tissue, or body fat—in overweight and obese women. This time, they looked specifically at women in the program, recruiting 200 women for six months of exercise training, nutritional counseling, and caloric reduction.

“How exercise interacts with insulin is not entirely clear, but there’s clearly an interaction between the two,” Cannon noted. “There’s some controversy in the field. Is it fatness, or fitness, or lack thereof [that determines outcome]? Some people think you can be fat and fit, and it’s just as good as being not fat. A lot of epidemiologists have looked at this over the years and shown that fitness does matter. Most of the trials are in men [and most show] that fit people do better over time.”

Preliminary data from 100 of the participants—a mix of black and white employees—has shown a significant relationship between BMI and insulin sensitivity. The two have an inverse relationship, with the higher BMI leading to lower insulin sensitivity. “Most of our participants are below the [insulin resistant line], with about 25% in the insulin resistant range,” Cannon explained. “BMI was a predictor of diminished insulin sensitivity.”

Researchers also found that there was a racial difference in what body types were the best predictors of diminished insulin sensitivity. For blacks, waist circumference was a strong predictor, while truncal fat was the strongest predictor for whites.

“Skeletal muscle may be less effective in oxygen consumption during exercise and less insulin sensitive in blacks compared with whites, contributing to poor fitness and insulin resistance, respectively, in black women,” Cannon noted.

The study also found that poor fitness plays an even larger role in non-insulin dependent glucose uptake in blacks and whites.

Currently the participants are set to enter the activity phase of the study, which involves 30 minutes of activity on most days, with caloric decrease and expected weight loss. Researchers will then examine whether these changes will have a demonstrable effect on patients’ health.

Asked why death by CV disease is decreasing in the face of the obesity and diabetes epidemic, Cannon predicted that the steady decrease the nation has experienced over the last few decades might be coming to an end. “That decrease is probably from better control of blood pressure, statins to control cholesterol, judicious use of revascularization and surgical heart treatments, and better drugs for treating acute coronary syndromes,” he explained. “But obesity is clearly working against this. I read editorials that speculate that now we’ll see an uptick in CV disease and that our children will not live as long as we are going to live, as they become more obesity and diabetes prone.”

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